A block copolymer refers to a copolymer consisting of a plurality of blocks or segments of repeating units distinct in characteristics from one another. It tends to be superior in characteristics to typical random copolymers or polymer blends. For example, the block copolymer may include both of soft elastic blocks (referred to as “soft segments”) and hard crystalline blocks (referred to as “hard segments,”) and thus have good properties, such as excellent elasticity and heat resistance. More specifically, such a block copolymer has elasticity at a temperature equal to or higher than the glass transition temperature of the soft segments and shows a thermoplastic behavior at a temperature higher than the melting temperature, so it can have relatively good heat resistance.
A specific example of the block copolymer, SBS (styrene-butadiene-styrene) triblock copolymers and their hydrogenated versions (e.g., SEBS) are known for their usefulness in a variety of applications since they have good characteristics regarding heat resistance and elasticity.
Recently, the use of olefin-based elastomers, which are a copolymer of ethylene/propylene and α-olefin, has been intensively under consideration. More specifically, many attempts have been made to use the olefin-based elastomers in a variety of applications, such as for use purposes as a substitute for rubber materials. For further improvement on the heat resistance of the olefin-based elastomers, there has been an attempt to use block copolymer type elastomers in place of the conventional random copolymer type olefin-based elastomers such as ethylene-α-olefin random copolymers.
In spite of those attempts, however, the study for commercialization of olefin-based elastomers with enhanced heat resistance has already reached its limit. Moreover, the conventional block copolymer type olefin-based elastomers also encounter a limitation in that they are susceptible to deterioration of processability during the melt processing. Accordingly, there have been consistent demands for olefin-based elastomers with enhanced heat resistance and processability.